Argenx drug developed to treat generalized myasthenia gravis, a rare neuromuscular disease, is now FDA approved, the first treatment in a new class of drugs that takes a new approach to treating autoimmune diseases.
Myasthenia gravis develops when the body makes autoantibodies that interfere with the way nerves and muscles communicate. The disease can lead to severe attacks of weakness that cause difficulty in swallowing and breathing that can be life threatening. The Argenx drug, efgartigimod, causes a reduction in antibody levels associated with myasthenia gravis. Argenx will market its new drug, the Dutch company’s first product, under the name ‘Vyvgart’.
There are therapies for early forms of myasthenia gravis. The class of drugs called acetylcholinesterase inhibitors stop the breakdown of a key neurotransmitter for muscle contraction, but they cause gastrointestinal side effects such as vomiting, diarrhea, and abdominal pain. This treatment is followed by corticosteroids and immunosuppressants. Steroids can cause bone thinning and weight gain, and can contribute to diabetes and high blood pressure, among other problems. Immunosuppressants can cause elevated liver enzymes and greater susceptibility to infections.
Treatments for advanced cases of myasthenia gravis include antibodies given intravenously and plasmapheresis, a procedure in which blood is drawn and filtered. Both treatments introduce the risk of complications.
The body has built-in ways of processing proteins, including antibodies. It regularly removes antibodies from the circulation by bringing them into cells where they are either broken down by the lysosome, which is a cellular elimination system, or recycled back into the circulation. A protein called the neonatal Fc receptor (FcRn) is key to this recycling process. The antibodies bound to the FcRn are recycled into circulation. Those that are not bound to FcRn are degraded by the cell’s elimination systems.
Vyvgart is an antibody fragment discovered and developed using Argenx’s proprietary technology, based on the llama immune system. Argenx engineered Vyvgart to bind to FcRn, which in turn prevents recycling of the antibodies that cause myasthenia gravis. Rather, these unbound antibodies go to the lysosome for degradation.
Vyvgart’s approval by the FDA covers adults who test positive for a particular antibody that causes loss of muscle function: the anti-acetylcholine receptor (AChR) antibody. Of the 65,000 patients with myasthenia gravis in the United States, about 17,000 of them are positive for the AChR antibody, Argenx said in a presentation to investors. This is the same group of patients referred by Soliris, a successful Alexion Pharmaceuticals treatment for several autoimmune diseases that has been approved for myasthenia gravis in 2017. The antibody drug Alexion works in a different way, binding to the complement system protein C5 to block the immune response that develops in myasthenia gravis.
Argenx tested Vyvgart in a Phase 3 placebo-controlled clinical trial involving 167 patients. The aim of the 26-week study was to assess patients according to a survey that assesses symptoms of myasthenia gravis. In the study, nearly 68% of patients treated with the drug Argenx responded to treatment compared to 30% of those given placebo. The results were also favorable for Vyvgart on a measure of muscle weakness. Last June, the results of the study were published in The Lancet Neurology.
Side effects reported in the study (respiratory tract infections, headaches, and urinary tract infections) were comparable in both arms. However, Vyvgart also binds to immunoglobulin G (IgG), an antibody that prevents pathogens from infecting the body. The FDA has warned that because the drug Argenx lowers IgG levels, patients face a greater risk of infection. Vyvgart’s drug label does not include a boxed warning for dangerous side effects.
Vyvgart is the first FDA-approved drug that works by blocking FcRn, but competitors are following closely with drugs targeting the same target. Earlier this month, UCB declared data a phase 3 test of its antibody targeting the FcRn injected subcutaneously, rozanolixizumab. Preliminary results showed that the drug achieved the primary objective of showing a statistically significant change in score according to the assessment of myasthenia gravis. The Belgian drug maker said regulatory submissions in the United States, Europe and Japan are expected in the third quarter of 2022.
Momenta Pharmaceuticals’ flagship drug nipocalimab was the centerpiece of Johnson & Johnson’s $ 6.5 billion acquisition of the company last year. The antibody targeting intravenously infused FcRn is under development for several autoimmune disorders, including myasthenia gravis.
Speaking on a conference call Friday, Argenx COO Keith Wood said Vyvgart’s annual net price for a typical patient would be $ 225,000. The actual price will vary based on several factors including the patient’s weight and number of treatment cycles required, as well as insurance coverage, discounts, and discounts. But Woods said Argenx has reached an agreement in principle with several national and regional payers. The agreement describes a value-based agreement, in which reimbursement of the product is linked to the benefit that the therapy demonstrates in a patient. Woods explained that the value-based deal will limit payers’ exposure to cover therapy for patients who need more medication.
Argenx has additional plans for its flagship drug. A version injected by the subcutaneous route is currently in the advanced testing phase with preliminary results expected in the first half of 2022. Clinical trials are also underway to evaluate efgartigimod in five other rare diseases. CEO Tim Van Hauwermeiren said Argenx aims to expand the use of its new drug to 15 indications by 2025.
Photo of the Argenx investor presentation